Mount Doom

Mount Doom, often known as Orodruin, is the colossal volcano located in Northern Mordor, and is infamous for being the location in which Sauron forged the One Ring in the Second Age.

Orodruin was the major explanation for Sauron building his home in Mordor during the Second Age. It is thought that he knew the fire and magma situated within the volcano could be used to strengthen his magic and power. Most notably used to forge the most powerful artifact in the history of Middle Earth, the One Ring.

Also, it seems that Sauron also combined his power with Orodruin, making more than a volcano. As his power grows, Mount Doom becomes more violent and volatile.